Two things: a fix for Time Machine always asking to use disks and – because of what you said about your work – a way to schedule Time Machine backups so they won’t impact the way you use your iMac.
Time Machine is a great utility for backups; if something happens to your hard drive, Time Machine will have a complete snapshot accurate to within an hour or so. But Time Machine is disk intensive, and by that I mean Time Machine is always working in the background, so with your video editing, that might be annoying and might slow down your work.
But you can solve that problem with TimeMachineEditor, which is a little program that lets you schedule your backups for time when your iMac is idle.
And it’s pretty easy to stop those requests to use every hard drive you plug in. Go to your Utilities folder and find Terminal, and start it up. At the prompt, type exactly
and then hit return. You won’t see any indication that the command finished, but after the next restart, Time Machine shouldn’t ask if you want to use any of your other disks for backup.
Also, see Apple’s site for more on Time Machine: Apple – Support – Mac OS X – Time Machine.